A pipe has a longitudinal axis. A flex board extends along the longitudinal axis within the pipe and curls around the longitudinal axis. A cross-section of the flex board perpendicular to the longitudinal axis has a flex-board curve shape that has a first section on a first side of a line perpendicular to the longitudinal axis and a second section on a second side of the line perpendicular to the longitudinal axis. The first section has a first section shape and the second section has a second section shape. A first conductive stripe is coupled to the flex board, extends along the longitudinal axis, and follows the contour of the first section of the flex board. A second conductive stripe is coupled to the flex board, extends along the longitudinal axis, and follows the contour of the second section of the flex board.